1. Field of the Invention
The present invention relates to a shape measuring instrument having a contact type measuring probe, more preferably, to a machine-mount type shape measuring instrument mounted on a processing machine.
2. Description of the Related Art
Japanese Laid-Open Patent Publication No. 7-260471 (hereinafter referred to as Related Art 1) and Japanese Laid-Open Patent Publication No. 2005-502876 (hereinafter referred to as Related Art 2) are incorporated herein by reference.
Conventionally, a shape measuring instrument for measuring a surface shape of an optical lens or the like has reduced a contact pressure to its required minimum so as not to damage a target. Such shape measuring instruments having reduced contact pressure is disclosed in Related Art 1 and Related Art 2 or the like, for example.
The shape measuring instrument of Related Art 1 will be described with reference to FIG. 6.
In Related Art 1, a contact pressure is adjusted while a measuring probe is maintained in a gravity direction, and gravity is balanced with a spring or the like. That is, the shape measuring instrument comprises, a measuring probe 32 which comes into contact with a target 180 vertically from above, a spring 152 for adjusting a gravity component of the measuring probe 32; and a position detector 154 for detecting a position of the measuring probe.
In addition, in Related Art 2, as shown in FIG. 7, a measuring probe 32 is inclined and maintained by supporting means 134, thereby reducing a contact pressure to the target 180. Adjustment of the contact pressure is made by using tilt adjusting means 136. In other words, this adjustment is accomplished by adjusting a tilt angle of the measuring probe 32.
However, the shape measuring instrument of Related Art 1 is of type of applying a measuring probe 32 to the target 180 from above, thus, making it difficult to mount a horizontal type ultra-precision processing machine which facilitates ejection of chips. In addition, it is difficult to control a measurement pressure due to spring nonlinearity. Therefore, there is a problem that the measurement pressure is changed due to a stroke position of the measuring probe.
On the other hand, in a shape measuring instrument of Related Art 2, a measurement pressure has not been easily changed successfully because the pressure has been adjusted by changing a tilt angle of a measuring probe 32. For example, at the time of measuring a target of a shape shown in FIG. 5, when a tilt face indicated by P2 is measured with respect to a case of measuring a planer position indicated by P1 (perpendicular face relevant to the measuring probe 32), a couple is applied to the measuring probe 32 resulting in some deflection, and a measurement error occurs. Thus, it is desirable to reduce a measurement pressure. However, it has been difficult to reduce the measurement pressure during measurement in Related Art 2. In addition, if the tilt angle of the measuring probe 32 is changed by tilt adjusting means 136, thereby adjusting the measurement pressure, a site at which the measuring probe 132 abuts against the target 180 is changed, and an error occurs.